1. Field of the Invention
The present invention concerns a method for positioning the level of a slice in the generation of a slice acquisition of an examination subject with an x-ray examination device. The invention also concerns a corresponding slice-level positioning device for positioning the level of a slice in the implementation of a slice acquisition of an examination subject with an x-ray examination device, as well as an x-ray examination device with such a device for positioning the level of a slice.
2. Description of the Prior Art
With appropriately equipped x-ray examination devices (referred to as “sliceable”) such as, for example, above-table examination devices, Bucky tables, or similar diagnostic procedure stations, it is possible to generate a slice exposure from an examination subject (for example, from a patient) in which, for the most part, only the structures located in a defined slice plane are clearly recognizable. In addition, the various parameters of the x-ray examination device are set such that all regions before and after the desired slice plane are blurred, i.e. they are recorded fuzzy, and only the structures in the slice layer are clearly reproduced. Selective information thus can be obtained about very definite organs or bone structures of a patient, for example the patella or the spinal canal. The slice level is the position of the desired slice plane in the radiation path between the x-ray radiator and the x-ray detector (which, in the cited diagnostic procedure stations, is normally located beneath the patient) and must be positioned as exactly as possible before the exposure by the operating personnel. For exact positioning of the slice level, and thus for exact orientation of the images of definite body slices of the patient detected with the help of slice exposure, slice-level indicators are generally used that project light crosses, laser markings, etc. onto the patient as an aid, and thereby visibly mark the actual slice level set on the device on the patient for the operator. In addition, a corresponding projection device is mounted on the x-ray examination device, for example on the patient positioning plate. Different exemplary embodiments of such slice level light beam localizers are described in German Patent 197 04 703, for example. Laser marking devices are also configured for other purposes such as, for example according to German OS 44 21 315, aid for a tumor position marking on the body of a patient before exchanging a computed tomography assembly on a therapy device.
A disadvantage of the known slice level indicators and devices for the positioning of the level of a slice, is that the operator must stay by the patient in order to exactly position the slice level with the aid of the slice level indicators. During the exposure, the operator must then leave the x-ray room for reasons of radiation protection. If a further slice recording is to be generated at another slice level, the operator must once again return to the patient in order to undertake a new positioning.